Simulation of the forward model of the deconvolution. The noisy data, d (Panel a), is the convolution of an extended object, o (Panel b), with the AO-corrected PSF of the instrument, p (Panel c), plus a nuisance term, n (Panel d). This term is composed of the acquisition noises (readout + photon), defective pixels (‘salt & pepper’ pattern), cosmic ray impacts (orange arrows), and signals from potential moons orbiting the main object (coloured circles). Panels a,b: to emphasise both the main body and the surrounding halo, a dual linear scale was used to insert the main body in its halo, as is noted by the ‘/’ in the colour bars. Panels b: photo of 67P/Churyumov–Gerasimenko by Rosetta (European Space Agency). Panels c: PSF obtained with ZIMPOL on HD16469 (P. Vernazza), normalised to peak at one for the display.